RE: 3rd Axis necessary?
If your shooting seriously on tough long hilly courses in 3-d,it is an absolute necessity in 3-d,atleast it is if you are wanting to win.
I do use my level when hunting.
The main reason it matters on hilly terrain is you will subconsciously start to align your bow with the terrain and if that terrain is at an angle,you will be off on your shot.Now you start to rely on the bubble to keep your bow level but if your bubble is lying to you,then you are leaning the bow because of the bubble.